1. Field of the Invention
The present invention relates to a recording-sheet supplying apparatus configured to supply recording sheets one by one, and relates to an image recording apparatus including the recording-sheet supplying apparatus.
2. Description of the Related Art
There is conventionally known an image recording apparatus, such as a printer and a facsimile, including a recording-sheet supplying apparatus in which a plurality of stacked recording sheets (hereinafter, may be referred to as sheets or cut sheets) are accommodated in a sheet tray, and each sheet is separated from the other sheets by a rotation of a sheet-supply roller, so as to be supplied to an image recording section from the sheet tray.
For example, Patent Document 1 (Japanese Patent Application Publication No. 2000-233836) discloses a recording-sheet supplying apparatus in which a drive shaft is disposed above a sheet tray so as to extend in a direction perpendicular to a sheet-supply direction, and in which an arm is pivotably supported on the drive shaft. In the apparatus, a free end of the arm points toward a sheet-separator portion provided at a distal end of the sheet tray. On a free end portion of the arm, there is mounted a sheet-supply roller for supplying each of sheets accommodated in the sheet tray. The arm is forced by a forcing spring such that the sheet-supply roller always contacts an uppermost one of the accommodated sheets irrespective of an amount (i.e., a height) of the sheets accommodated in the sheet tray. The sheet-supply roller is rotated by a rotational force transmitted from the drive shaft via a rotation transmission mechanism provided on the arm.
In the image recording apparatus as disclosed in the Patent Document 1, the sheet-supply roller is rotated in a predetermined direction, whereby a plurality of the sheets in the sheet tray are supplied. Then, an uppermost one of the sheets is separated from the other of the sheets when the supplied sheets pass through the sheet-separator portion.
Meanwhile, as shown in FIG. 10A, in the recording-sheet supplying apparatus, the sheet-supply roller 102 disposed at a distal end portion of the arm 100 which is pivoted about a drive shaft 101 provided at a basal end of the arm 100 always presses the uppermost sheet 103. Thus, where a relatively large amount of the sheets 103 are accommodated in the sheet tray, an angle of inclination of the arm 100 with respect to a surface of the uppermost sheet 103 (more precisely, an angle α between the surface of the uppermost sheet 103 and a line connecting a point at which the sheet-supply roller 102 contacts the sheet 103 and a pivot center of the arm 100) is relatively small. The angle of the inclination (i.e., the angle α) becomes larger with decrease in the amount of the sheets 103 accommodated in the sheet tray.
The contacting pressure of the sheet-supply roller 102 with respect to the sheet 103, and an applying force of the sheet-supply roller 102 with respect to the sheet 103 vary in accordance with the angle α of the arm 100. That is, where the relatively large amount of the sheets 103 are accommodated in the sheet tray (where the angle α is relatively small), the applying force becomes relatively small, and the contacting pressure becomes lower. Thus, a no-sheet feeding, in which the sheet-supply roller 102 supplies no sheet 103 during its operation even though at least one of the sheet 103 is accommodated in the sheet tray, is more likely to occur. In contrast, where the relatively small amount of the sheets 103 are accommodated in the sheet tray (where the angle α is relatively large), the applying force becomes relatively large, and the contacting pressure becomes higher. Thus, a multi-sheets feeding of the sheets 103 is more likely to occur.
To solve the above-described problems, in the image recording apparatus as disclosed in Patent Document 1, a downstream end portion of a bottom plate of the sheet tray which plate is disposed substantially horizontally is raised so as to be nearer to the sheet-separator portion. However, a mechanism for raising the downstream end portion of the bottom plate is disposed between a main body of the image recording apparatus and the bottom plate of the sheet tray, thereby complicating a structure of the image recording apparatus and requiring a relatively large space. As a result, the image recording apparatus is unfortunately upsized.
On the other hand, as disclosed in Patent Document 2 (Japanese Patent Application Publication No. 2006-306619) for example, an image recording apparatus of a recent type is configured, in order to lower a height thereof, such that an auxiliary sheet tray (a second sheet tray) configured to accommodate small-sized sheets (e.g., post cards) in a state in which the sheets are stacked on each other is provided above a main sheet tray (a first sheet tray) configured to accommodate recording sheets (e.g., plain sheets) in a state in which the recording sheets are stacked on each other, and such that the auxiliary sheet tray can be advanced and retracted. Further, as the image recording apparatus of the recent type, there is known an image recording apparatus including a first sheet-feed device for the main sheet tray, and a second sheet-feed device for the auxiliary sheet tray. The first sheet-feed device has a first arm and a first sheet-supply roller while the second sheet-feed device has a second arm and a second sheet-supply roller. The first arm and the second arm are pivotably supported by one drive shaft.
In the image recording apparatus having the two arms, the auxiliary sheet tray is disposed such that a bottom plate of the auxiliary sheet tray is above a surface of an uppermost one of the sheets in the main sheet tray with a prescribed vertical space in a state in which a maximum amount of the sheets are accommodated in the main sheet tray. In an image recording apparatus disclosed in Patent Document 2, the first arm is longer than the second arm such that a range of an angle of the inclination of the first arm with respect to a surface of an uppermost one of the sheets in the main sheet tray and a range of an angle of the inclination of the second arm with respect to a surface of an uppermost one of the sheets in the auxiliary sheet tray are almost the same, that is, such that a range of an angle between the surface of the uppermost sheet in the main sheet tray and a line connecting a pivot center of the first arm and a point at which a sheet-supply roller provided in the first arm contacts the sheet, and a range of an angle between the surface of the uppermost sheet in the auxiliary sheet tray and a line connecting a pivot center of the second arm and a point at which a sheet-supply roller provided in the second arm contacts the sheet, are almost the same.